Method and apparatus for completing oil wells and the like



Nov. 17, 1959 R. c. LISTER 2,

METHOD AND APPARATUS FOR COMPLETING on. WELLS AND THE LIKE Filed on. s. 1956 "'-"INVENTOR.

FIG.3 vRowas l.l-J-s rtil'i ATTORNEY METHOD AND APPARATUS FOR COMPLETING OIL WELLS AND THE LIKE Application October 9, 1956, Serial No. 614,883

5 Claims. (Cl. 166-42) The present invention relates to a method and apparatus for use in completing wells for the production of oil, gas and the like;

In the operations of drilling and completing oil and gas wells, a bore is drilled through that formation of earth which contains gas and oil-bearing sands, and a casing then is inserted into and extended almost the entire length of the bore. A slurry of cement is pumped into the casing, and a portion of the cement is forced out the bottom of the casing and thence upwardly into the annular space between the casing and the wall of the well bore to a distance considerably above the gas or oil producing formation. The casing is thus sealed off from the oil and gas as well as foreign substances such as water, and precludes communication between the several formations.

In order to force the cement slurry through the casing and up about the casing into the annulus, large pressures are'necessary. The cement slurry is displaced from the casing by inserting a piston of rubber commonly referred to as a cementing plug into the cylindrical casing and forcing the piston downwardly by hydraulic pressure or other suitable pressure means, thereby pushing the cement slurry before the piston. The downward move-' ment of the piston is arrested by a baffle plate inserted in a coupling or joint between two adjoining sections of casing at a point above the oil or gas producing zone. Thus from the amount of cement used and the position of the bafiie, the final position of the cement in the annulus may be roughly calculated.

After the cement has set, the standard procedure is to drill away the cementing piston, baflie and a portion of the cement within the casing to an extent such that the casing is clear and open to a point below the oil or gas producing zone but substantially above the bottom of the casing. In order that the casing may be opened to the flow of oil or gas, it is necessary to perforate it opposite the oil or gas producing zone. This has heretofore been accomplished, albeit imperfectly, by means of a multishot bullet gun which fires a multitude of bullets in different directions through the casing, or by a jet or shaped charge gun which utilizes a high velocity force stream in a plurality of places and so provides perforations through the casing. After perforations have been formed in the casing, it is not difiicult to break up the thinv shell of cement in the bore surrounding the casing perforations by means of hydraulic pressure, if the ocment has not already been broken by the means used for piercing the casing.

The bullet gun and jet gun methods of piercing the wall of a casing have many disadvantages: They are expensive; they require elaborate equipment and highly skilled workers, they are often at least partially unsuccessful, and they induce long fractures or cracks in the protective cement. When an insuflicient number of perforations has been created by means of a bullet gun or jet gun, the slow infusion of oil or gas into the casing constitutes the only means whereby the-inadequacy can be States Patent 2,913,051 Patented Nov. 17,1959

ascertained. By then it is extremely diflicult to pump the oil or gas back into the formation and, while maintain to the applicant by which the nature and number of the casing apertures may be inspected or determined prior to the entrance of oil or gas into the casing. 1

The principal object of this invention is to provide a method and an apparatus by which the above-mentioned.

disadvantages and limitations of the bullet gun and jet gun methods may be successfully overcome.

Another object of the invention is to provide a method and an apparatus which will eliminate the need for using guns or similar devices and enable the desired communication between a producing formation and a cemented casing to be established by the final drilling operation which is used for removing cement from the casing. 1

According to this invention, the operations attendant to the completion of oil wells and the like are carried out by the provision and use of a casing section that is preformed with a multiplicity of perforations and adapted to be located opposite the oil or gas producing formation, so as to afford a means of communication for the desired flow of oil or gas from the formation into the easing, and these perforations are initially closed by plugs which extend inwardly into the space of the casing so that they will be engaged and dislodged by a drilling tool when cement is removed from the casing in the final drilling operation. The plugs seal the casing section against the passage of cement through the perforations as the cementing of the well takes place, yet they are dislodged from the perforations and broken up and removed from the well by the action of the drilling tool in the course of the cement drilling operation.

The plugs may be made of a metal such as aluminum or iron, or of a molded plastic composition, or of some other suitable solid and drillable material. They should extendinwardly from the perforations into the casing section for a distance at least equal to the width of the perforations, so as to provide a body or stem upon' which the drill will be assured of acting to dislodge them from the perforations. If desired, they may be simply pressed or force-fitted into the perforations, or they may be threaded thereinto so that the threads will be broken or stripped to free the plugs under the action of the drill. A particularly satisfactory procedure is to drill aligned openings in opposite sides of the casing and insert an elongated or tube-like plug into each pair of these openings so that each plug forms a bridge across the perforated casing section. When a drilling tool is used to remove cement from a casing section so constructed, the tool dislodges and breaks or grinds up each of the plugs, thereby creating a multiplicity of open perforations through the wall of the casing opposite the producing formation.

After the perforations have been freed of plugs, hydraulic pressure can be applied to break up the outer layer of cement in the bore surrounding the casing near the perforations. Communication thus provided with the productive formation, the oil will flow into the casing, without any need for the use of a bullet gun or'a jet gun.

invention and in the accompanying drawing forming a part hereof, wherein:

Fig. 1 is a side elevational view, partly broken away and in axial, vertical section, of a casing section embodying the present invention;

Fig. 2 is an end view of the casing section of Fig. 1; and

Fig. 3 is a diagrammatic side elevational view, partly broken away and in axial, vertical section, of the lower portion of a well casing in place in an oil or gas well bore with the perforated casing section of Fig. 1 located at the producing formation.

Referring to the drawing in detail, Fig. 1 shows a well casing section 13 having screw threads 8 formed at both ends for use in coupling section 13 with other sections of a well casing. Section 13 is made of steel or other suitable metal.

. Cut at intervals in the wall of section 13 are many perforations 9. The perforations 9 are formed in pairs with the perforations of each pair located in alignment at opposite sides of the casing section. Each pair of perforations is stoppled by an elongated plug 16, of metal, plastic or other suitable material, which extends diametrically across the interior of casing 13. The plugs 16 here shown are rods of a metal such as aluminum, which are removable from the respective perforations and disintegratable by the action of conventional rotary oil well cement drilling tools. The diametric extension of the plugs 16 is best revealed in Fig. 2, from which it will be apparent that adjacent pairs of perforations lie in different horizontal and different vertical planes. This is so that the perforations will not cause a weakness in any one side of the casing and that the oil or gas will have varied means of ingress into the casing.

In Fig. 3 a series of cylindrical casing sections 7, 13 and 12 are shown in the bore 17, which has been drilled into the earth to a substantial distance below the oil or gas producing formation at 11. The various casing sections are joined to each other by means of couplings 15, which engage the screw threads 8 formed in the ends of each casing section. A conventional baflle plate or collar 14, usually made of metal such as cast iron, has been inserted in the joint between casing sections 7 and 13 and forms a circular projection to limit the descent of a cementing piston 6, which fits within the casing section 7 and cooperates closely with the inner surface of the wall thereof. Casing section 13 is identical with that described in Fig. '1, while conventional casing sections are shown at 7 and 12.

The apparatus described aboveis utilized in the following manner: After the casing has been located in the well bore, with the plugged section 13 set opposite the producing formation, a cement slurry is pumped into the casing to a level well above the baffie 14. The usual rubber cementing piston 6 then is inserted into the casing 7 and pumped downward so as to force the column of cement downward through the open lower end of the casing, from which the cement flows into the space at that end and upwardly through the annular space around the several casing sections to a level well above the oil or gas producing formation 11. When the piston 6 contacts baffle 14, its downward movement is arrested, so thata part of the cement column remains in the casing below the baflle.

The cement is now permitted to harden and form a protective seal and anchor for the casing. When hardened, it seals the lower end of the casing and the casing section at the producing formation from the entrance of water or other foreign substances from other strata exposed to the well bore. Since a barrier of cement remains in casing section 13, a well drilling tool is now inserted into the casing and operated from the surface of the well to drill out all obstructions within the casing to a desired low level. The drill breaks up and removes the piston 6, the baffle 14 and the cement barrier beneath the baffie. In its descent, the drilling tool also tears the plugs 16 out of their apertures 9 and breaks or drills up these plugs which are removed from the well, thus opening the perforations 9v so that the casing may have full access to the producing formation.

The drilling process is continued until the cement barrier and the plugs 16 have been dislodged and removed to the desired extent. With the perforations in the casing section 13 now unplugged, suitable means such as hydraulic pressure is applied within the casing section and through the perforations 9 to break up the outer layer or shell of cement between the perforations and the producing formation. When this is accomplished, oil from the producing formation 11 will be free to flow past the broken up cement shell and through the open perforations 9 into casing section 13. Thus, the well is now ready for production.

While only a preferred embodiment of the invention has been illustrated and described, it will be understood that the new features and principles herein disclosed are not restricted thereto, but may be embodied in various other forms within the purview of the appended claims. For example, the plugs which close the apertures need not necessarily extend across the entire diameter of the casing section, but only so far as to be contacted and removed by a well drill.

What is claimed is:

l. A casing element for an oil or gas well, adapted to be located at the producing formation of'a well bore substantially above the bottom of the well casing, then cemented in place and thereafter opened laterally to' receive fluid from the'formation, comprising a tubular section of easing having a multiplicity of perforations preformed in and spaced about the wall thereof for draining fluid from the formation into said section, and a multiplicity of plugs seated in said perforations and blocking the passage of fluid therethrough between the internal space and the exterior of said section, said plugs being dislodgeably held in said perforations and extending from them into the internal space of said section, said plugs being'removable from said perforations and disintegratable, by the action of a well cement drilling tool to open said perforations to the flow of fluid therethrough betweenrsaid internal space and the formation.

2. A casing element for an oil or gas well, adapted to be located at the producing formation of a well bore substantially above the bottom of the well casing, then cemented in place and thereafter opened laterally to receive fluid from the formation, comprising a tubular section of easing having a multiplicity of perforations preformedin and spaced about the wall thereof for draining fluid from the formation into said section, and a multiplicity of plugs seated in said perforations and blocking the passage of fluid therethrough between the internal space and the exterior of said section, each of said plugs extending across the internal space of said casing section and having its ends dislodgeably held in a pair of said perforations at opposite sides of said section, said plugs being removable from said perforations and disintegratable by the action of a well cement drilling tool to open said perforations to the flow of fluid therethrough between said internal space and the formation.

3. A casing element for an oil or gas well, adapted to be located at the producing formation of a well bore substantially above the bottom of the well casing, then cemented in place and thereafter opened laterally to receive fluid from the formation, comprising a tubular section of casing having a multiplicity'of perforations preformed in and spaced about the wall thereof for draining fluid from the formation into said section, and a multiplicity of plugs seated in said perforations and blocking the passage of fluid therethrough between the internal space and the exterior of said section, each of said plugsextending horizontally and diametrically across the internal space of said casing section and having its ends dislodgeably held in a pair-of said perforationsat opposite sides of said section, said plugs being removable from said perforations and disintegratable by the action of a. well Qernent drilling tool to open said perforations.

to the flow of fluid therethrough between said internal space and the formation.

4. In a method of completing oil wells and the like in which a casing is extended into a well bore through a producing formation and is cemented by forcing cement through its lower end and thence upwardly between the casing and the wall of the bore, the steps which comprise locating at said formation a tubular section of said casing, said section being preformed with a multiplicity of perforations, each of which is closed against the passage of fluid therethrough between the internal space and the exterior of said section by a dislodgeable plug seated therein and extending inwardly therefrom into the internal space of said section, thereafter flowing cement downwardly through the casing around and past said plugs and from the lower end of the casing upwardly between the casing and the wall of the well bore to a location above the producing formation, thus filling said casing with cement to a level above said plugs, then hardening the cement, and thereafter drilling cement from within said section and by the action of the drill simultaneously dislodging and removing said plugs from said perforations to open said perforations for the flow of fluid therethrough.

5. In a method of completing oil wells and the like in which a casing is extended into a well bore through a producing formation and is cemented by forcing cement through its lower end and thence upwardly between the casing and the wall of the bore, the steps which comprise locating at said formation a tubular section of said casing, said section being preformed with a multiplicity of perforations, each of which is closed against the passage of fluid therethrough between the internal space and the exterior of said section by a dislodgeable plug seated therein and extending inwardly therefrom into the internal space of said section, thereafter flowing cement downwardly through the casing around and past said plugs and from the lower end of the casing upwardly between the casing and the wall of the Well bore to a location above the producing formation, thus filling said casing with cement to a level above said plugs, then hardening the cement, thereafter drilling cement from within said section and by the action of the drill simultaneously dislodging and removing said plugs from said perforations to open said perforations, and then forcing a fluid under pressure from within said section through said perforations to disrupt the cement outside the casing between said perforations and the producing formation.

References Cited in the file of this patent UNITED STATES PATENTS 64,546 Lewis May 7, 1867 389,164 Putney Sept. 4, 1888 1,613,105 Helm Jan. 4, 1927 2,173,033 Armentrout et a1. Sept. 12, 1939 

